Adult Hydra attenuata with vitally stained gastrodermal cells were dissociated into their component cells which were then randomly reaggregated into pellets by low-speed centrifugation. Representative examples of these preparations, which develop into normal adult hydra if left undisturbed, were examined fresh at low magnification and at higher magnification in fixed, stained, and sectioned specimens. The actual pellet stage lasts less than 1 hour because the adult ectodermal and gastrodermal cells rapidly sort themselves into an inner and outer layer and seem to secrete a new mesoglea immediately thereafter. The "embryo" becomes trilaminar and attains a central cavity by extruding a large amount of cellular debris at the end of the first day. At about this same time, new tentacles begin to differentiate from rapidly dividing and undifferentiated interstitial cells. Regulation of tentacle number and position occurs at the end of two days, and the body form is essentially reestablished within 60 hours by further differentiation of the hypostomes and body wall. Complete separation of the preparation into individual polyps does not occur until about 190 hours of development.
Prenatal exposure to excess vitamin A (160,000 USP units/day) from days 15 through 19 of gestation results in altered lung morphology, characterized by thickened septal walls and/or large areas of atelectasis and an associated high neonatal mortality. Marked variability in both morphological and physiological expression from this prenatal insult is commonly seen between litters and littermates, making analyses difficult. The present study documents morphological intralitter variation observed in vitamin A-exposed 2-day-old rats as compared to controls. Representative midhilar coronal histological sections of each lung were examined by two methods and the results compared. The first method, although less sensitive, demonstrated that five out of eight experimental rat lungs had a significantly greater percentage of tissue to airway space as compared with undisturbed controls (greater than 43%). The second method, using several morphological criteria and a grid system to score parenchyma into classifications based on the degree of morphological variation and projected functional capability, clearly found significantly increased percentages of poor or nonfunctional lung tissue (P greater than 0.01) in seven out of eight pups exposed to excess vitamin A. This method of ranking the severity of adverse effects on tissue morphology allowed identification of drug-affected newborn and provided a means to quantify the alterations. Such a means for identifying affected individuals from littermates is essential to research methodologies for detecting substances which, when administered during fetal life, produce decrements of postnatal function but no gross structural abnormalities.
Fetal exposure to excess vitamin A results in a highly variable degree of lung pathology and high neonatal mortality in the Long-Evans rat. The present study evaluated O2 consumption in newborn of vitamin A-treated, vehicle-treated, and untreated pregnancies on five consecutive postnatal days beginning with the day of delivery (D0). Pregnant female rats were treated by gavage with 160,000 USP units of retinyl acetate dissolved in 0.5 ml corn oil on days 15 through 19 of gestation. Vehicle and undisturbed controls were run concurrently. All animals delivered spontaneously, and the pups were tattooed and individually tested in a closed system consisting of three chambers submerged within a thermostatically controlled water bath at 33 degrees C. Vitamin A-exposed pups, as a group, have significantly lower QO2 (ml O2 consumed/min/kg body weight) values than controls through postnatal day 2 (p less than 0.05). By days 3 and 4 of age, the mean QO2 values of surviving vitamin A-treated pups were similar to those of controls. A QO2 of 30 or greater on day 0 appears to be critical for early neonatal survival of vitamin A-exposed pups, as 87% of the pups with initial QO2 less than 30 died prior to day 4. Oxygen consumption rates in teratogen-exposed pups exhibiting low QO2 on day 0 rarely reached normal levels. In contrast, the occasional control pup with such low initial levels were well within normal limits (means +/- 1 SD) by the following day.(ABSTRACT TRUNCATED AT 250 WORDS)
In the presence of vinblastine, the sorting of individual cells proceeded normally but mesogleal formation was delayed. The “embryo” became highly distended and failed to expel a central mass of unused or residual cells as occurs during regeneration of “embryos” that have not been treated with a test chemical. The epithelial cells became vacuolated and failed to maintain their sheetlike arrangement and attachments, although they did begin secretion of basement membrane. Interstitial cells failed to increase in number.
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